Patent GB-834785-A (GB)
Title: Improvements in and relating to back e.m.f. responsive electric circuit arrangementsand electric motor control systems
Inventor: ASBURY ALLAN
IPC: B65H23/185
Filed: 1955-06-17
Abstract: 834,785. Automatic winder-control systems. ENGLISH ELECTRIC CO. Ltd. June 18, 1956 [June 17, 1955], No. 17548/55. Class 38 (4). In an arrangement comprising a D.C. motor 60, Fig. 6, and a reference source 63 connected with resistors 70, 72 to form a bridge and in which output means 73 responsive to the difference in currents I and I 2  flowing in the two networks produces a signal depending on the deviation of the motor B.E.M.F. from the reference value, the ratio. of the values of resistors 64, 70, in the two networks is equal to the ratio of the resistive volt drop through the motor 60 to the voltage proportional to armature current developed across resistor 72. In the winder control system, Fig. 1, wherein the tension in a wound element is maintained constant by maintaining constant the current of the winder motor armature 10a and keeping the B.E.M.F. equal to a reference voltage, generated in a tachometer generator 12, which is proportional to the strip speed, control winding 17a of a magnetic amplifier 17 is energized in accordance with the potential differences across points E and B of the circuit comprising the winder motor armature 10a, field winding 10b and resistors 13, 14, the resistors 13 and 14 having a ratio equal to the ratio of the resistive volt drop in the motor armature circuit and the voltage across the field winding 10b. The control signal output of the magnetic amplifier 17 effects coarse control by means of motor-operated field regulator 19, 20 and fine control by supplementary excitation of field 10d, and rectifiers 15, and 21 permit only an increase in excitation during coiling. The field regulator is arranged not to fall back during stoppages and manual switching (not shown) is provided to permit only a decreasing excitation during uncoiling. The supplementary field 10d assists the main field during coiling and opposes it during uncoiling. Armature current control is effected by the regulation of the field 11b of the generator 11 in accordance with the difference between the potential of the point E and the output of the reference exciter 23 which is excited from the D,C. bus-bars, an additional circuit comprising magnetic amplifier 27 and rectifiers 25, 26 being provided to reduce the field during strip breakage and thus prevent undue acceleration of the motor. The additional circuit is also effective whilst slack is being taken up during initial wrapping of the element, a switch 28 being provided to shortcircuit rectifier 26 during this time in order to increase the sensitivity. A shut-down relay 29 is provided to operate when the output of amplifier 27 exceeds a predetermined value and it is prevented, by an isolation switch 30, from operating during starting. In a modification, Fig. 2 (not shown), the generator field is energized by the difference in outputs of a reference exciter and a current exciter which is energized by a field carrying the winder motor armature current. A modification for reducing interaction between magnetic amplifiers 27 and 17 wherein the control winding of amplifier 27 is connected to a tapping on a resistance network shunting the resistors 13, 14 is described with reference to Fig. 3 (not shown). In a further modification, Fig. 4, the magnetic amplifier 17 is replaced by a magnetic amplifier 80 which is of the push-pull type wherein the output varies both in magnitude and sense with the error, and resistor 16 is shunted by a rectifier 81 to render the system more sensitive to wrap and break, a potential being developed across a resistor 82 in the field of the current reference - exciter 23 to reduce the exciter output under such conditions. The field 11b in this modification is fed by the sum of the voltages developed across the points A, B and the output of the exciter 22 to produce a field which is substantially the same for all strip speeds. A resistor 24 provides manual control of the strip tension. Specification 811,571 is referred to.